People often abuse public pay telephones. Pay telephones also suffer abuse from the environment which is often laden with dust, chemicals and corrosive agents. The hook switch assembly is the recipient of much of the abuse. Typical hook switch assemblies include a hook switch lever for supporting the telephone receiver when the telephone is not in use, and typically contains several sets of switch contacts.
One problem with conventional hook switch assemblies is that the switch contacts, which are often leaf switches, are delicate and subject to damage or malfunctioning from dust or excessive motion. The excessive motion often results when the pay telephone is operated by rapidly or forcefully removing or replacing the receiver onto the hook switch lever. To limit the motion transmitted to the switch contacts, some conventional pay telephones limit the motion or travel of the hook switch lever. In addition, the contacts are typically positioned so that overtravel does not occur when the hook switch lever is operated. While repositioning the contacts may overcome the overtravel problem, it creates a new problem in that any wiping action of the switch contacts may be reduced or limited. As will be known to those skilled in the art, the wiping action of electrical contacts tends to keep the contacts clean, which is important in a dusty environment.
Dust and other environmental contaminants which might affect the operation of the switch contacts can enter the hook switch assembly through the opening in the telephone housing for the hook switch lever. One approach to reducing this problem is to physically isolate the switch contacts from the hook switch lever. Isolation has been accomplished in the past by forming cavities in the telephone housing, and by placing the hook switch lever in one cavity and the switch contacts in a separate cavity spaced apart from the hook switch cavity.
While isolating the switch contacts from the hook switch lever minimizes the exposure to dust, it does not completely eliminate all dust and the contacts will eventually become dirty and must be cleaned or replaced. In some conventional pay telephones, the telephone unit has to be disassembled to obtain access to the contacts for cleaning or replacement. It will thus be understood there is a need for a hook switch assembly wherein the contacts have a self-cleaning action which prolongs the life of the contacts, and wherein the need for disassembly and cleaning has been minimized.
Some conventional hook switch assemblies have contact arrangements with a relatively high number of parts. Since each part represents a potential trouble spot, it is beneficial to keep the number of parts as small as possible. U.S. Pat. No. 4,572,930 discloses a hook switch uses a plurality of movable terminals and a plurality of stationary terminals. U.S. Pat. No. 4,456,799 and related U.S. Pat. Nos. 4,436,964 and 4,424,420 disclose a hook, switch assembly which uses alignments of contact operating springs which are paired with a cam resting between opposed leaf springs.
Yet another hook switch assembly has the switch contacts enclosed in a plastic housing which minimizes the exposure to dust. However, this particular arrangement requires a lever controlled by a slotted program card to operate the contacts; the program card is operated by a cam which is actuated in response to motion of the hook switch lever. The program card is delicate and has been found in practice to fail often. Moreover, for the switch contacts to operate properly the cams and levers must be precisely aligned. It will be understood that it would be highly desirable to provide a cam switch assembly which minimizes the number of parts and is easy to align.
It is possible on some pay telephones to make calls by rapidly operating the hook switch lever to simulate the pulses of a typical telephone dial. To overcome this problem of hook switch dialing and prevent unauthorized calls from being made, some hook switch assemblies include a mercury switch which prevents hook switch dialing. U.S. Pat. No. 3,365,554 discloses such a mercury switch along with two cam operated leaf switches. In addition to being expensive, mercury is a hazardous, toxic, material. Understandably, it is highly desirable to have a hook switch assembly which prevents hook switch dialing without using mercury.